Analysis of bending mechanism in multi-scanning laser bending process based on plastic strain development

By using multi-pass straight-line scan strategies, a larger bending angle can be achieved. There is, however, a limited understanding of the variation in bending angle per pass during multi-pass under various process parameters. In multi-pass laser scanning, the bending angle cannot always linearly increase with scanning passes and this phenomenon can be observed mostly in low heat input. Strain hardening is the common explanation for this phenomenon. However, it could not explain why this bending angle reduction phenomenon occurs at low heat input scanning rather than at high heat input scanning. In this study, this phenomenon is discussed based on strain development in experiments and numerical simulation. The different growing mechanism of plastic strain is analyzed to reveal the effects of laser power and scanning velocity. Furthermore, the opposite bending trend that occurred at larger laser power is discussed in comparison to the plastic strain development. The study shows that relatively larger heat input below 6.7 J/mm can help to avoid the bending angle reduction phenomenon and the opposite bending trend is highly dependent on the larger laser power. For achieving the expected cumulative bending angle in multi-pass laser bending, it is recommended to decrease the scanning velocity at a relatively low laser power level while increase the scanning velocity at a high level of laser power.